How do I install Clearcase bridge and Version importer into my existing RTC Eclipse client 6.0?

The ClearCase bridge and importer are two different ways to integrate ClearCase with RTC. You need to decide which way you'd like to use. The article https://jazz.net/library/article/813 explains the two methods in details.
To setup the environment, you can also refer to Knowledge Center:
http://www.ibm.com/support/knowledgecenter/SSYMRC_6.0.0/com.ibm.team.connector.scm.cc.doc/topics/c_sync_intro.html
http://www.ibm.com/support/knowledgecenter/SSYMRC_6.0.0/com.ibm.team.connector.scm.cc.doc/topics/c_bridge_intro.html

I'd suggest first looking at the on-line help page:
http://www.ibm.com/support/knowledgecenter/SSYMRC_6.0.0/com.ibm.team.connector.scm.cc.doc/topics/c_getting_started.html

What that will tell you is:
- The version importer is not an Eclipse plug-in ... it is a command line tool.  So you do not install it into Eclipse ... you invoke the exports and imports via command line commands.
- To use the ClearCase Bridge, you load the ClearCase Remote Client plug-in into your Eclipse client containing the RTC plug-in.